1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive comprising an asynchronous partition located on a disk between two isochronous partitions.
2. Description of the Prior Art
Disk drives may store both asynchronous and isochronous data. Asynchronous data is transferred to and from the disk drive within a “best-effort” time interval, whereas isochronous data is transferred to and from the disk drive within a “time-constrained” time interval. An example of isochronous data is audio/video (AV) data transmitted from the disk drive to a monitor for viewing. The AV data must be transmitted within a prescribed time interval in order to avoid interruptions during the viewing session. An example of asynchronous data is user application data, such as word processing documents, accounting documents, etc., manipulated by an end user of a host computer. The transfer of asynchronous data to a host computer can be interrupted (within some maximum time-out period) without significantly degrading the performance of the host application.
Disk drives also typically employ error correction code (ECC) circuitry for correcting errors on-the-fly in both the isochronous and asynchronous data. If the ECC circuitry is unable to correct errors in asynchronous data, the disk drive typically performs various firmware retry procedures in an attempt to correct the errors. The latency of the firmware retry procedures is tolerated since it does not significantly degrade the performance of the host application while ensuring the host application receives error-free data. If asynchronous data cannot be recovered using the retry procedures, the disk drive responds with an error message rather than transfer bad data to the host computer. In contrast, if the ECC circuitry is unable to correct errors in isochronous data, the isochronous time constraints typically preclude using the firmware retry procedures to correct the errors. This is not a significant problem since occasional errors in the isochronous data do not significantly degrade the performance of the typical isochronous application, such as streaming AV data to a monitor. Therefore the isochronous data, including the errors, is typically transmitted by the disk drive to the host computer rather than respond with an error message.
The disk within an isochronous/asynchronous disk drive is typically divided into an isochronous partition for storing the isochronous data and an asynchronous partition for storing the asynchronous data. An isochronous communication protocol, such as the AV/C protocol, is used to access the isochronous partition according to the specified time constraints, and an asynchronous communication protocol, such as the SBP-2 protocol, is used to access the asynchronous partition in a best-effort manner. The asynchronous communication protocol may also be used to access the isochronous data in a best-effort manner, for example, to edit a selected portion of a video program.
It is desirable to support the concurrent (interleaved) transfer of both asynchronous and isochronous data to and from the disk drive. If the isochronous and asynchronous partitions are contiguous as illustrated in FIG. 1, the maximum seek distance may be from the inner diameter track of the disk to the outer diameter track. If the disk drive is directed to make multiple interleaved accesses to data located at the ends of the partitions, the cumulative seek times may interfere with access to the time-constrained isochronous data. In addition, if the disk drive is required to frequently seek between the asynchronous and isochronous data in order to satisfy the isochronous time constraints, performance in accessing the asynchronous partition may degrade.
There is, therefore, the need to ameliorate the inherent latency of seek times in a disk drive which can interfere with the time-constrained access of isochronous data while concurrently accessing asynchronous data.